Electrical Capacitance Tomography (ECT) is the reconstruction of material concentrations of dielectric physical properties in the imaging domain by inversion of capacitance data from a capacitance sensor.
Electrical Capacitance Volume capacitance imaging or ECVT is the direct 3D reconstruction of volume concentration or physical properties in the imaging domain utilizing 3D features in the ECVT sensor design. ECVT technology is described in U.S. Pat. No. 8,614,707 to Warsito et al. which is hereby incorporated by reference.
Adaptive Electrical Capacitance Volume Tomography (AECVT) provides higher resolution volume imaging of capacitance sensors based on different levels of activation levels on sensor plate segments. AECVT is described in U.S. Patent Application Publication US2013/0085365 A1 to Marashdeh et al. which is hereby incorporated by reference.
Post-tensioning is a method of reinforcing concrete, or other materials, with high strength steel strands or bars. Post-tensioning tendons are assemblies comprised of an outside sheathing or duct, the strands or bars, and any grout or other coating surrounding the strands or bars. Post-tensioned tendons systems are often used to reinforce segmental concrete structures and provide load bearing capacity. The tendons are typically anchored, stressed, and pumped with grout. The tendon forms a continuous bond along its length with the grout surrounding it. The bond is achieved through a cementitious matrix which surrounds the steel strands. The matrix acts with the polymer cylindrical container (duct) which encases the concrete member to complete the bond path between the prestressed strands and the grout member. When the grout hardens, through its bond to the steel strands, it locks the movement of the strands within the tendon to that of the grout surrounding it. Hence, the force in a bonded tendon becomes a function of the deformation of the concrete surrounding it. Long term reliability of the tendon requires continuous grout and bonding throughout the tendon. Discontinuities like air pockets (e.g., voids), un-cured grout (e.g., water), and partially-cured grout (e.g., bleeding grout) along the tendon weaken the tendon's ability to maintain its load and may eventually result in failure of the tendon. Discontinuities within the tendon's grouting system can lead to section loss (e.g., corrosion of the steel), broken wires and cables, undermining the integrity of a tendon system.
To assure tendon structural integrity, tendons must be inspected after grouting and periodically throughout the life of the structure. This requires an imaging technology that is able to make three-dimensional images of the inside of the tendon, to detect air, water, and bleeding grout pockets, to estimate volume of detected pockets, and to identify their location. The technology must be economical to employ and capable of producing acceptable images of discontinuities. Ideally, it should not use radiation that would require shielding to protect the operator and the users of the structure. Electrical Capacitance Volume Tomography (ECVT) satisfies these criteria. It's features include safety, high imaging speeds, light weight sensor design, and higher resolution imaging with use of AECVT sensors.
The present invention provides an innovative ECVT sensor and supporting features for inspecting tendons and cable stays in bridges and structures. The present invention can also be used to image other similar construction-type structures such as pipelines. It also provides a method for using ECVT sensor results for locating discontinuities in structures and rusted steel, and estimating their volume and location. The preferred embodiment of the present invention also involves an innovative design for the construction of an ECVT sensor that has the ability to travel along the length of a tendon using wireless control. The developed ECVT sensor preferably surrounds, or substantial surrounds, the tendon in order to make three-dimensional images and is adapted to open up easily for mounting and dismounting. In the preferred embodiment, it has modular design and can be fitted with a traction (movement) module to make it capable of autonomous travel. The design is scalable to accommodate larger and smaller tendons. It preferably incorporates a suspension mechanism that accommodates a specified range of tendon diameters. It also preferably employs a position tracking mechanism based on counting rotations of tractor wheels.
The present invention also provides an AECVT design using capacitance plates having a plurality of individually addressable segments with variable voltage distribution for detection of steel degradation using multi-frequency excitation. The integrative and adaptive data acquisition method is used to activate the ECVT sensor plates with different frequencies for detection and volume identification of rusted steel or broken steel cable strands.